Key message

Round goby has established to several coastal areas of the Baltic Sea and is spreading to new areas.The species has become the predominant fish species in several areas, has caused habitat shifts of competing fish species and potentially caused local depletion of blue mussels.

Results and assessments

Current status in the Baltic Sea

Round goby is an invasive species of Ponto-Caspian origin, first observed in the Baltic Sea in Gulf of Gdansk, in 1990, likely arrived via ship Ballast water (review by Sapota 2006). Currently it has been found or established in the southern and eastern Baltic Sea, Bothnian Sea, Gulf of Finland, Archipelago Sea, Kattegat and Belt Sea and southern Sweden (Figure 1).

Figure 1. Presence of Round goby in the Baltic Sea. Please note that the map has been drawn using
agreed HELCOM assessment units ​and does not reflect the actual distribution; e.g. in some assessment units, such as Swedish west coast and Finnish Bothnian Bay, single observations result in the classification of "present" for the whole area. Source: HELCOM List of non-indigenous species.

Population densities

In the Gulf of Gdansk, being the most likely source of the Baltic invasion, the density of four fish per m2 has been observed (Sapota & Skora 2005). Densities are lower in deeper water.

Round goby density along the Latvian open Baltic Sea coast is 1-3 fish per m2 at 14 m depth. More data about the Round goby density at different depths will soon become available through the GES-REG project.

Invasion history

The first record of the Round goby in Polish waters is from the tip of Hel Peninsula (Gulf of Gdansk) in 1990 (Skóra, Stolarski 1993). The species abundance has increased, especially in the western part of the Gulf of Gdańsk, Puck Bay, where it settled into habitats occupied by indigenous Gobius niger(Jażdżewski and Konopacka 2002). In 1994 the fish was reported to be present in almost the whole of the Polish part of the Gulf of Gdańsk, whilst already in the next year the first individuals were found outside the Gulf (Kuczyński 1995).

In 1999, the species was found for the first time in the Polish part of the Vistula Lagoon (ICES 2004) and German Rügen area (Sapota 2006). In 2002, the species was found in the Gulf of Riga, in 2003 along the entire German coast, and in 2005 from the Gulf of Finland and Archipelago Sea (reviewed in Sapota 2006, Ojaveer 2006).

In 2008, the first observation was made in Bornholm and southern Sweden, Hanö bight and in 2009 in the coast of Helsinki. In 2010, it had invaded the Belt Sea and in 2011 the Round goby was detected from Mariehamn and the Bothnian Sea.

According to latest reports, N. melanostomus is expanding up along the middle and western parts of the Polish coastal zone of the Baltic Sea (Psuty 2010). The biological and ecological features of the species will predispose it to a continuation of its expansion. According to Björklund and Almquist (2010), local sub-populations of the species are differentiating genetically in the southern Baltic Sea.

Role in the food web

The ecology and reproductive biology of the species is reviewed by Sapota (2006). In brief, Round goby is a mussel feeder, feeding also on arthropods, and therefore competes with flatfish and eelpout. In the Gulf of Gdansk, both of these native species have slightly shifted their feeding habitat to deeper waters as a result of increased Round goby density (Karlson et al. 2007). According to the review by Kornis et al. (2012), the mussels comprise 65-89% of the diet of Round goby.

It is suspected that the high densities of Round goby in the Lithuanian coast have depleted locally dense blue mussel banks (Darius Daynus, pers. comm.). A similar finding was made by in the Latvian open coast inside the MPA Nida-Perkone (Solvita Strake, pers. comm.).

Round goby is the main food item for cod and perch in the Gulf of Gdansk (Almquist et al. 2010). The species is also an important prey item for Great cormorant and Grey heron, contributing locally up to 60-95% of the prey number (Bzoma 1998, Bzoma & Stępniewicz 2001, Jakubas 2004).

Round goby is a preferred catch by fishermen in Poland and within its native range. It is considered tasty and it may gain popularity as a catch also elsewhere in the invasive range.

The Baltic Sea Action Plan does not directly have an ecological objective for the distribution and abundance of non-indigenous species. The management objective 'No new introductions of non-indigenous species' addresses the new introductions and the ecological objective 'Thriving communities of plants and animals' addresses the whole community. Nonetheless, this fact sheet gives essential background information for the other HELCOM BSEFS and supports risk assessments of NIS in the region.

Metadata

Data source: In the HELCOM Ballast Water Road Map, HELCOM HABITAT and MONAS were requested to compile a list of non-indigenous, cryptogenic and harmful native species in the Baltic Sea by the end of 2008. The list is a living document which has been edited in various HELCOM subsidiary bodies, expert workshops and projects. Since 2008 the list has been modified by HELCOM HABITAT (11/2009 and 12/2010), HELCOM MONAS (12/2009), the HELCOM HOLAS project and, most recently, by the HELCOM CORESET project.

The presence and absence of NIS in the assessment units is confirmed by experts and non-confirmed presence or absence is also shown. The list contains references to justify the information, but quite often the justification is made by expert judgement.

The Baltic Sea area was divided into 60 areas and each expert noted the presence or absence of each NIS. Presence is a sign of the species ever being found in the area. It does not indicate that it is still present and does not indicate the abundance.

Geographical coverage: The information has been gathered from the entire Baltic Sea from all sources of information, from research studies and national monitoring.Experts of the HELCOM CORESET project have recommended to regularly monitor ports and areas of intensive ship traffic in order to follow the effectiveness of the IMO Ballast Water Convention.

Temporal coverage: The abundance information may contain old records of non-established populations. The HELCOM List of non-indigenous species contain presence-absence information from historical sources and current situation.Quality of information Data is variable in time and space, sometimes anecdotal, but even without full coverage of information the quality of information received from research studies is reliable. The list of presence from the expert group is not totally substantiated with references, and need to be complemented with that

References

Anon., 2008: Directive 2008/56/EC of the European Parliament and the Council of 17 June 2008 establishing a framework for community action in the field of marine environmental policy (Marine Strategy Framework Directive). Official Journal of the European Union, L 164/19, 25.06.2008.

Bzoma, S., Stempniewicz, L., 2001: Great cormorants (Phalacrocorax carbo) diet in the Gulf of Gdansk in 1998 and 1999. Third International Symposium on Functioning of Coastal Ecosystems in Various Geographical Regions, June 19-22, 2001 Institute of Oceanography, University of Gdansk.